Power supply unit for bipolar power supply

ABSTRACT

The invention relates to a power supply unit for bipolar power supply of a plasma technology or surface technology system having at least one controllable d.c. power supply (G 1,  G 2 ), whose positive and negative outputs are connected to the input of at least one bridge circuit of electronic power switches (T 1  to T 4 ), said power switches being connected on the input side to at least one control signal conditioning device and on the output side to at least one current detection circuit for the open-/closed-loop control of the power switches, and being connected to the load of the system (A). By means of this invention, current pulses having freely variable amplitudes (V o+ , V o− ) can be generated for the positive and negative current pulses by providing for each bridge circuit (T 1  to T 4 ) at least two d.c. power supplies (G 1,  G 2 ), and the positive output of the two d.c. power supplies is connected in series in each case by two power switches (T 1  and T 4;  T 2  and T 3 ) to the negative output of the other power supply (G 2,  G 1 ), where the output of the bridge circuit for the system in each case has a tap between the power switches of the two series circuits.

[0001] The present invention relates to a power supply unit for thebipolar supply of power to a plasma technology system or a surfacetechnology system as set forth in the preamble of claim 1. Such units,as are disclosed for example in EP 534 068 B, generally comprise a d.c.main power supply whose outputs are connected to the inputs of a bridgecircuit of electronic power switches. The power switches are connectedto control signal conditioning devices that control the power switchesin the desired manner in order to obtain a desired pulse pattern for theplasma system. The unit has separate control signal conditioning devicesto individually regulate the control times for the positive and negativeoutput signals, allowing any impulse shape to be selected.

[0002] The object to the invention is to improve upon a prior-art powersupply unit in such a way as to increase the degree of freedom inselecting a desired pulse shape. In the invention, this object isaccomplished with a power supply unit of the type set forth in thepreamble through the characteristic elements of claim 1. A furtherobject of the invention is to create an apparatus that permits anydesired pulse shapes to be supplied at frequencies into megahertz range.This object is accomplished by an apparatus as recited in claim 7.

[0003] The dependent claims set forth advantageous embodiments of theinvention.

[0004] In the invention at least two d.c. power supplies must be usedfor each bridge circuit. The bridge is divided, insofar as a seriescircuit comprising two power semiconductors is interposed between thepositive output of the first d.c. power supply and the negative outputof the second d.c. power supply.

[0005] The same applies to the negative output of the first d.c. powersupply and to the positive output of the second d.c. power supply,between which a series circuit comprising two power semiconductors isconnected. The tap for the pulses sent to the plasma system always islocated between the two power switches in the series circuits.

[0006] In this way, the amplitudes of the positive and negative pulsescan be freely selected—for example, corresponding to a desired signalpattern.

[0007] If, in addition, separate control signal conditioning devices areprovided to individually control the various power switches, it is notonly possible to select any desired amplitudes of the positive andnegative pulses, it is also possible to select their switching time andsignal pauses or dead times. Thus, the greatest possible degree offreedom for selecting a pulse pattern to be sent to a plasma system isprovided.

[0008] Since these systems have to be able to switch a very highcurrent, the effective range of the power supply units is limited to afrequency range of about 100 to 200 kHz. By using a plurality of powersupply units connected in parallel, preferably two to eight, andsynchronously controlling the individual power supply units withcorrespondingly short timing offsets, it is possible to achieve anydesired pulse pattern with a frequency extending into the megahertzrange if, for example, eight units having a frequency of 125 kHz areused. The devices are preferably controlled by means of a control bus atthe control input of the individual units. In this case, the controlsignals from a central control unit are sent to the single individuallyaddressable units.

[0009] To accomplish this, the individual power supply units arepreferably provided with an address or ID code that allows thesystematic response of each individual current power supply unit to becontrolled.

[0010] The outputs of the d.c. power supplies are preferably stabilizedby capacitative means using capacitors that have the highest possiblecapacitance in order to be able to provide very high pulse currents. Ifthe power supply units are being operated near the limit of theirmaximum capacitance, the dead time between the pulses can be limitedwithout constraints.

[0011] A bridge can preferably be connected between the negative outputsas well as between the positive outputs of each of the two d.c. powersupply units, so that it is possible to switch to conventionaloperation, however such conventional operation does not permit thepositive and negative pulse amplitudes to be individually controlled.

[0012] The maximum permissible current dynamics for the switchabletransistors and free-wheeling diodes is adjusted by means of twooutput-side inductances L1 and L2. In this way the pulse current is readand evaluated dynamically. In particular, with very low-impedance shortcircuits, it is necessary to quickly determine the amount of excesscurrent and to shut off the transistors as soon as possible, in order toprevent damage to the semiconductor layer, to the substrate surfaces, orto the plasma coating system.

[0013] The power supply unit of the invention or the apparatus comprisedof power supply units, can be used for all plasma-technology processessuch as CVD, plasma PVD, magnetron sputtering, plasma nitriding, andplasma etching.

[0014] The invention is described below based on the schematic diagram.The schematic diagram shows:

[0015]FIG. 1 a greatly simplified wiring diagram of a power supply unitof the invention, without control circuitry,

[0016]FIG. 2 an illustration of the output pulses of the bipolar powersupply of the invention,

[0017]FIG. 3 a schematic diagram of an apparatus of the invention havinga plurality power supplies,

[0018] FIGS. 4A-F possible pulse patterns created by the apparatus shownin FIG. 3, and

[0019]FIG. 5 an apparatus comprising a plurality of power supplies thatprovides an alternative to FIG. 3.

[0020]FIG. 1 shows a power supply unit having two d.c. power suppliesG1, G2, whose outputs are stabilized by capacitors C1, C2. Voltage V1 isapplied to d.c. power supply G1, while voltage V2 is applied to d.c.power supply G2. The positive output of the first d.c. power supply G1is connected to the negative output of the d.c. power supply G2 by meansof two power switches T1, T4 connected in series. In a similar manner,the negative output of the first d.c. power supply G1 is connected tothe positive output of the second d.c. power supply G2, by means of twopower switches T2, T3 connected in series. The outputs going to a plasmasystem A are attached in the middle between the series circuits T1, T4,T2, T3 and are limited with regard to current dynamics by inductancesL1, L2, in order to protect the power switches as well as the plasmasystem itself and the substrates SU contained in it. A current consumeris connected to the output of the power supply unit. Its output signalis sent to a controller (not shown) used to control the power switchesT1 to T4 in order to achieve closed-loop control-in other words, afeedback-controlled control system.

[0021] The placement of two bridges S1, S2 between the positive outputsand between the negative outputs of the two d.c. power supplies G1, G2allows the power supply unit to be operated in a conventional manner,albeit with identical amplitudes for the negative and positive currentpulses. For example, the following operating modes may be set:

[0022] D.c. voltage DC+when T1 and T2 are closed, while T3 and T4 areopen.

[0023] D.c. voltage DC−when T3 and T4 are closed while T2 and T2 [sic]are open.

[0024] Unipolar plus pulsed UP+when T1 and T2 are pulsed, while T3 andT4 are open.

[0025] Unipolar negative pulsed UP−when T3 and T4 are pulsed while T1and T2 are open.

[0026] Bipolar pulsed BP, when T1 and T2 alternatively are clocked withT3 and T4.

[0027]FIG. 2 describes the pattern over time of a possible pulse patternwith the power supply unit of the invention of FIG. 1. Time is plottedon the horizontal axis in microseconds. The vertical axis shows thevoltage of the output pulses in the positive and negative directions.The figure shows an initial positive pulse having an output voltage ofV₀₊ and a pulse duration of T_(on+), followed by an off-time T_(off+).An initial negative pulse having an amplitude of V⁰⁻ and a pulseduration of T_(on−) follows this off-time, followed by the off-timeT_(off−). The four pulse time parameters T_(on+), T_(off+), T_(on−), andT_(off−) during a period can be freely selected independently of eachother, whereby currently, when conventional technology is being used,the total of the times in a period must not exceed 8 microseconds(corresponding to a frequency of max. 125 kHz).

[0028]FIG. 3 shows an apparatus for generating high-energy,high-frequency pulse trains having frequencies extending into themegahertz range. The apparatus comprises a plurality of power supplyunits as shown in FIG. 1, which are identified in this figure by thereferences “System 1, System 2, . . . System N.” The outputs of saidplurality of power supply units, preferably 2 or 3 or up to 20 powersupply units, are connected in parallel and are routed to the input of aplasma system A. In order to synchronize and control the individualpower generation units, a central controller 10 is provided. It isconnected via a data bus to the control connections of the individualpower supply units. Since in this system each power supply unit, System1 to System N, has its own identification or address, the centralcontroller 10 can individually control each power supply unit in theapparatus. Instead of using addressability, the controller of course mayalso be individually connected to each power supply unit by means ofseparate supply lines.

[0029] In addition, power consumers 14 are provided in the paralleloutput ahead of the feed into system A. Their outputs are connected tothe central controller 10 in order in this manner to obtain feedback tocontrol the controller. The signal shapes shown in FIGS. 4A to F can begenerated by means of this apparatus, which is shown in FIG. 3. Thepolarity of the train of individual pulses as well as amplitude andduration of these pulses, as well as the dead times between the pulses,can be set separately and individually. In this way, high-energy,high-frequency pulse patterns having frequencies extending up into themegahertz range can be generated. As shown, for example, in FIG. 4B,sine curves can be approximated. As shown in FIG. 4A triangular curvescan be approximated. FIG. 4D shows an approximated sawtooth curve in abipolar train.

[0030] Of course, the pulses from the various generation units System 1. . . System N can also be sent, overlapping one another in time, sothat brief high-power pulses can be produced, albeit at a lowerfrequency.

[0031] The apparatus can also be used to generate desired pulse shapesby means of a kind of Fourier transformation, a technique which may beused to transform a plasma in a coating system into a desired excitationform. In the freely configurable setting of the pulse pattern with anN-tuple pulse-parallel connection of N power supply units, certainfrequency spectra can be superimposed additively or removed by adding orremoving individual pulse components.

[0032]FIG. 5 shows a system that is largely identical with FIG. 3, andin it identical or functionally equivalent parts have the same referenceidentifiers. However, in FIG. 5, unlike in FIG. 3, the electrodes of theindividual power supply units SYSTEM 1 . . . SYSTEM N are not connectedin parallel, but are arranged according to a specified layout, forexample circular, in the treatment chamber of the plasma system. Thisnot only allows the pulse shape of the incoming current pulses to beset, it also allows the geometric development of the plasma to beinfluenced.

[0033] Instead of individual power supplies G1, G2, power supplies canalso be connected in parallel or in series. The use of the connectioncircuit described above is not limited to the power supplies specifiedabove. It can also be implemented with all types of high-power powersupplies, in order to obtain high-frequency high-power power supplieswith any desired pulse trains.

What is claimed is:
 1. A power supply unit for bipolar power supply of aplasma technology or surface technology system having at least onecontrollable d.c. power supply (G1, G2), whose positive and negativeoutputs are connected to the input of at least one bridge circuit ofelectronic power switches (T1 to T4), said power switches beingconnected on the input side to at least one control signal conditioningdevice and on the output side to at least one current detection circuitfor the open-/closed-loop control of the power switches, and beingconnected to the load of the system (A), wherein for each bridge circuit(T1 to T4) at least two d.c. power supplies (G1, G2) are provided, thepositive output of the two d.c. power supplies is connected in series ineach case by two power switches (T1 and T4; T2 and T3) to the negativeoutput of the other power supply (G2, G1), whereby the output of thebridge circuit for the system in each case has a tap between the powerswitches of the two series circuits.
 2. The unit of claim 1, whereinseparate control signal conditioning devices (12, 13) are provided toindividually control the positive and negative output signals, which arecombined in separate closed-loop control circuits, that are controlledindependently of one another by a controller (18).
 3. The unit of claim1 or 2, wherein the electronic power switches (T1 to T4) are produced byMOSFETs.
 4. The unit of claim 1 or 2, wherein the power switches (T1 toT4) are bipolar transistors IBGTs or other fast-switching electronicpower semiconductors.
 5. The unit of one of the above claims, wherein,the output from the two d.c. power supplies (G1, G2) is stabilizedcapacitatively (C1, C2).
 6. The unit of one of the above claims,wherein, at least one switch (S1, S2) is provided for switching the d.c.power supplies (G1, G2) in parallel.
 7. The unit of one of the aboveclaims, wherein, a controller for the separate open- and closed-loopcontrol of the d.c. power supplies (G1, G2) is provided.
 8. An apparatushaving a plurality of units of one of the above claims, characterized bya central controller (10) for simultaneously controlling and/orsynchronizing the output pulses issued by the individual units (SYSTEM
 1. . . SYSTEM N), in which the outputs of all units to the system (A) areconnected in parallel.
 9. The apparatus of claim 8, wherein, the centralcontroller (10) is connected to control inputs provided on the units(SYSTEM 1 . . . SYSTEM N) by means of a bus system (12), and preferablyis also connected to a current detection circuit (14).
 10. A process forgenerating current pulses for plasma technology and surface technologysystems using a device of one of claims 1 to 6, whereby the currentpulses having freely configurable system times (T_(on−), T_(off+),T_(off−), T_(off−)] are generated for the positive as well as thenegative current pulses and separately selectable amplitudes (V_(o+),V_(o−)) are generated for the positive and negative current trains. 11.The process for generating high-frequency current pulses for plasmatechnology and surface technology systems with an apparatus of claim 7or 8 that comprises a plurality of units, in particular between 3 and20, where the units are controlled by the central controller that isused to generate a coherent signal train, in which each unit is causedto generate a signal pulse, whose pulse time is, at most, equal to thetotal time of the signal pattern divided by the number of units.